Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 251951
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
251 PM CDT SAT OCT 25 2014

.DISCUSSION...
237 PM CDT

//SHORT TERM//
REST OF TODAY THROUGH SUNDAY... QUIET WEATHER REMAINS ON TAP FOR
THE REMAINDER OF THE WEEKEND AS UPPER LEVEL RIDGE TRANSLATES EAST
ACROSS THE AREA THROUGH THE PERIOD. SURFACE RIDGE IN PLACE FROM
THE NORTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY THIS
AFTERNOON WILL ALSO TRANSLATE EAST ACROSS THE AREA...BECOMING
CENTERED OVER NORTH CENTRAL ILLINOIS BY THE EARLY MORNING HOURS
SUNDAY. WITH DEWPOINTS MIXING OUT INTO THE LOW/MID 30S ACROSS
PORTIONS OF THE OUTLOOK AREA TODAY...ALONG WITH LIGHT WINDS AND
MOSTLY CLEAR SKIES IN PLACE TONIGHT...THE STAGE WILL BE SET FOR
STRONG RADIATIONAL COOLING OVERNIGHT. BLENDED OVERNIGHT LOWS
HEAVILY TOWARDS THE GEMNM/GEMNMBC WHICH APPEARS TO CAPTURE SOME OF
THE TYPICAL COOL SPOTS WEST OF THE FOX RIVER VALLEY WELL...AND
VERIFIES WELL UNDER THIS SYNOPTIC SITUATION.

JET STREAM BEGINS TO BUCKLE IN THE WEST AS A WAVE MOVES ONSHORE
OVER THE PAC NW AND CARVES OUT A TROUGH OVER THE GREAT BASIN BY
SUNDAY EVENING. MEANWHILE...AT THE SURFACE...BROAD LOW PRESSURE
WILL DEVELOP OVER THE FRONT RANGE OF THE ROCKIES WITH SOUTHWEST
FLOW ALOFT DEVELOPING SUNDAY EVENING. LOCALLY...DAYTIME HOURS WILL
BE DRY SUNDAY UNDER THE INFLUENCE OF THE DEPARTING SURFACE RIDGE
BUT EXPECT AN INCREASE IN CLOUD COVER FROM MIDDAY ON AS MID LEVEL
WARM ADVECTION STARTS TO OVERSPREAD THE REGION.

SUNDAY NIGHT THROUGH TUESDAY...
SURFACE LOW REMAINS UNORGANIZED SUNDAY NIGHT AS BROAD TROUGHING
MOVES EAST INTO THE UPPER MIDWEST...HOWEVER MODELS CONTINUE TO
ADVERTISE A 40-50 KT LOW LEVEL JET DEVELOPING ACROSS THE MID
MISSISSIPPI VALLEY WITH A DECENT PUSH OF MOISTURE INTO THE REGION
WITH PWATS OF AROUND 1.1 INCHES ADVECTING INTO THE AREA. ON THE
NOSE OF THE LOW LEVEL JET EXPECT THE POSSIBILITY OF SOME SHOWERS
AND THUNDERSTORMS TO DEVELOP WHERE THERE IS SOME MODEST ELEVATED
INSTABILITY PRESENT. THE CORRIDOR WHERE THE BETTER INSTABILITY AND
FORCING LINE UP STILL FAVORS AREAS NORTH OF THE CWA...HOWEVER
CANNOT RULE OUT PRECIP BUILDING DOWN INTO THE NORTHERN COUPLE
TIERS OF COUNTIES IN ILLINOIS. THE SURFACE LOW BEGINS TO DEEPEN
AND BECOME BETTER ORGANIZED MONDAY INTO MONDAY NIGHT AS THE UPPER
LEVEL TROUGH PUSHES INTO THE UPPER MIDWEST. LOW LEVEL CONVERGENCE
STRENGTHENS ALONG THE COLD FRONT AT THIS TIME...AND THE CHANCES
FOR SHOWERS AND THUNDERSTORMS INCREASE MONDAY EVENING AND NIGHT AS
THE COLD FRONT SWEEPS ACROSS THE AREA. BOTH THE GFS AND NAM NOW
ADVERTISE SOME PREFRONTAL ACTIVITY DURING THE DAY MONDAY...HOWEVER
SOUNDINGS SHOW FAIRLY NEGLIGIBLE INSTABILITY AND DRY LOW/MID
LEVELS. NOT SURE HOW MUCH PRECIP WOULD BE POSSIBLE GIVEN THE
SOUNDINGS SO WILL CAP ANY POPS AT 20 BEFORE 00Z. TAKING A STEP
BACK AND LOOKING A TEMPS MONDAY...GUIDANCE CONTINUES TO ADVERTISE
AN ANONYMOUSLY WARM THERMAL RIDGE THOUGH HAS ACCELERATED THE
TIMING OF THE RIDGE SOME FROM PREVIOUS RUNS. NUDGED TEMPS SLIGHTLY
TOWARDS THE LATEST BIAS CORRECTED ECMWF/GEMNH BUT DIDNT MAKE ANY
BIG CHANGES...STILL CALLING FOR MID TO UPPER 70S NORTH OF I-80 AND
UPPER 70S WITH POSSIBLY A FEW 80S TO THE SOUTH. BEHIND THE COLD
FRONT ON TUESDAY...THE H85 ZERO DEGREE ISOTHERM WILL APPROACH THE
AREA. WHILE TUESDAY SHOULD BE DRY BEHIND THE COLD FRONT...BREEZY
AND COOLER CONDITIONS ARE EXPECTED WITH AFTERNOON HIGHS ONLY IN THE
LOW TO MID 60S.

//LONG TERM//
WEDNESDAY THROUGH SATURDAY
MODELS CONTINUE TO ADVERTISE A HIGH AMPLITUDE PATTERN DEVELOPING
BY LATE IN THE WEEK WITH A SHOT OF ARCTIC AIR PUSHING TOWARDS
THE AREA...MORE AGGRESSIVELY NOW THAN COMPARED TO GUIDANCE 24 HOURS
AGO. THE LOW PRESSURE SYSTEM THAT IMPACTS OUR AREA EARLY THIS WEEK
WILL CONTINUE TO DEEPEN AS IT LIFTS ACROSS JAMES BAY WEDNESDAY
WITH COLD AIR STARTING TO WRAP AROUND INTO THE NORTHERN GREAT
LAKES. STRONG HIGH PRESSURE THEN BUILDS DOWN OVER THE CANADIAN
PRAIRIES AND SINKS SOUTHEAST TOWARDS THE UPPER MIDWEST. THE AIRMASS
IS QUITE COLD WITH GUIDANCE NOW SHOWING -10C TEMPS AT H85 SINKING
INTO NORTHERN ILLINOIS BY FRIDAY. DID NOT DEVIATE FROM A GENERAL
MODEL CONSENSUS BLEND GIVEN IT IS STILL A WAYS OUT...BUT THESE
TEMPS MIGHT BE TOO WARM IF CURRENT MODEL TRENDS HOLD.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY NW WINDS WITH GUSTS AROUND 24 KT THRU THE LATE AFTN.

JEE

//DISCUSSION...UPDATED 18Z...

GUSTY NW WINDS ARE EXPECTED THIS AFTN WITH MAX GUSTS APPROACHING
25 KT. HIGH PRESSURE MOVES OVERHEAD TONIGHT SO WINDS WILL QUICKLY
DIMINISH THIS EVENING TO LIGHT AND VARIABLE OVERNIGHT. FOG IS NOT
EXPECTED TONIGHT AS THE AIRMASS WILL DRY OUT TODAY. WINDS BECOME S
TO SE BEHIND THE RIDGE TOMORROW AFTERNOON WITH SPEEDS LESS THAN 10
KT. VFR CONDITIONS ARE EXPECTED THROUGHOUT THE FORECAST PERIOD.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

MONDAY...VFR/WX NIL BY DAY...SHRA/TSRA LIKELY MONDAY NIGHT. BREEZY
SOUTH WINDS.

TUESDAY...CHC SHRA/TSRA EARLY. MVFR POSSIBLE EARLY. WEST WINDS.

WEDNESDAY...VFR/WX NIL. WEST WINDS DAYTIME...BECMG SLY WEDNESDAY
NIGHT.

THURSDAY...SLIGHT CHANCE SHRA DAYTIME. VFR. SOUTHWEST WINDS
VEERING TO NLY BY EARLY EVENING AND OVERNIGHT.

FRIDAY...VFR/WX NIL. NORTH WINDS.

KREIN

&&

.MARINE...
251 PM CDT

LOW PRESSURE CROSSING JAMES BAY THIS AFTERNOON WILL CONTINUE
EASTWARD WHILE WEAKENING AS IT MOVES INTO SOUTHERN QUEBEC TONIGHT
AND SUNDAY. HIGH PRESSURE ACROSS THE NORTHERN PLAINS AND UPPER
MISSISSIPPI RIVER VALLEY WILL SLIDE SOUTHEASTWARD TONIGHT WHICH WILL
ALLOW THE PRESSURE GRADIENT ACROSS MUCH OF LAKE MICHIGAN TO TIGHTEN
LEADING TO AN INCREASE IN WEST TO NORTHWEST WINDS TONIGHT. WINDS
HAVE UNDER PERFORMED THROUGH EARLY AFTERNOON ACROSS MUCH OF THE
REGION BUT ARE STARTING TO COME UP INTO SMALL CRAFT ADVISORY RANGE
ACROSS THE ILLINOIS NEARSHORE WATERS SO WILL MAINTAIN THE CURRENT
SMALL CRAFT. WILL ALSO KEEP THE SMALL CRAFT FOR THE INDIANA WATERS
THROUGH SUNDAY MORNING WITH WINDS TURNING NORTHWESTERLY AND
INCREASING LEADING TO AN INCREASE IN WAVES. WILL EVALUATE STARTING
THE ADVISORY A FEW HOURS LATER CLOSER TO NEARSHORE ISSUANCE TIME.

WINDS SETTLE DOWN SUNDAY AS RIDGING PASSES OVERHEAD BUT LOW PRESSURE
WILL BE DEVELOPING ACROSS THE CENTRAL AND NORTHERN PLAINS AND WORK
INTO THE UPPER GREAT LAKES LATER MONDAY. SOUTHEAST WINDS WILL PICK
UP MONDAY AHEAD OF THE LOW THEN SHIFT WESTERLY WITH THE PASSAGE OF A
COLD FRONT MONDAY NIGHT. THE LOW WILL CONTINUE NORTHEAST AND DEEPEN
WHILE CONSOLIDATING ACROSS CENTRAL AND SOUTHERN ONTARIO. A SECOND
FRONT WILL TURN WINDS MORE NORTHWESTERLY TUESDAY NIGHT. SOUTHERLY
WIND GUSTS SHOULD BE TEMPERED AHEAD OF THE FIRST FRONT WITH A VERY
WARM AIRMASS LIMITING MIXING. GUSTS WILL INCREASE BEHIND THE FRONT
WITH COLDER AIR SPREADING IN. NOT A CLEAR SIGNAL FOR GALES RIGHT NOW
WITH THE LOW FAIRLY BROAD BUT SIMILAR SYSTEMS HAVE PRODUCED A SHORT
PERIOD OF STRONGER UNDERFORECAST WINDS SEVERAL TIMES THIS SEASON SO
WILL NEED TO MONITOR THIS CLOSELY IN THE NEXT DAY OR SO. HIGH
PRESSURE WILL THEN BUILD IN WEDNESDAY.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM SUNDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 5 PM SATURDAY.

&&

$$

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